1. Field of the Invention
The present invention relates to a method for determining and varying the capacity and data rates of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. There have been developed magnetic heads that have a write element for magnetizing the disks and a separate read element for sensing the magnetic fields of the disks. The read element is typically constructed from a magneto-resistive material. The magneto-resistive material has a resistance that varies with the magnetic fields of the disk. Heads with magneto-resistive read elements are commonly referred to as magneto-resistive (MR) heads.
Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
Information is typically stored in radial tracks that extend across the surface of each disk. Each track is typically divided up into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks. The number of tracks on a disk is dependent on the width of the heads. Smaller heads will allow for more tracks. Wider heads will produce less tracks. The number of tracks is sometimes defined in terms of tracks per inch (“TPI”).
The heads of a disk drive read and write data at a predetermined data rate sometimes defined in terms of bits per inch (“BPI”). Before shipping an assembled drive the heads are tested to insure that a head does not fall below a threshold bit error rate (“BER”). The BER of a head is measured while testing at an operating BPI. If the BER is below the threshold value then the drive is considered defective.
It would be desirable to provide a method for testing and adjusting the TPI and BPI of the heads to increase the yield of hard disk drives.